Method and apparatus for processing video signal

ABSTRACT

A method for decoding a video according to the present invention may comprise: decoding information indicating whether illumination compensation is performed for a current block, determining an illumination compensation parameter of the current block when the information indicates that the illumination compensation is performed for the current block, obtaining a prediction block by performing inter prediction for the current block, and performing the illumination compensation on the current block using the illumination compensation parameter.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage Patent Application of PCTInternational Patent Application No. PCT/KR2017/006976 (filed on Jun.30, 2017) under 35 U.S.C. § 371, which claims priority to Korean PatentApplication No. 10-2016-0085014 (filed on Jul. 5, 2016), the teachingsof which are incorporated herein in their entireties by reference.

TECHNICAL FIELD

The present invention relates to a method and an apparatus forprocessing video signal.

BACKGROUND ART

Recently, demands for high-resolution and high-quality images such ashigh definition (HD) images and ultra-high definition (UHD) images haveincreased in various application fields. However, higher resolution andquality image data has increasing amounts of data in comparison withconventional image data. Therefore, when transmitting image data byusing a medium such as conventional wired and wireless broadbandnetworks, or when storing image data by using a conventional storagemedium, costs of transmitting and storing increase. In order to solvethese problems occurring with an increase in resolution and quality ofimage data, high-efficiency image encoding/decoding techniques may beutilized.

Image compression technology includes various techniques, including: aninter-prediction technique of predicting a pixel value included in acurrent picture from a previous or subsequent picture of the currentpicture; an intra-prediction technique of predicting a pixel valueincluded in a current picture by using pixel information in the currentpicture; an entropy encoding technique of assigning a short code to avalue with a high appearance frequency and assigning a long code to avalue with a low appearance frequency; etc. Image data may beeffectively compressed by using such image compression technology, andmay be transmitted or stored.

In the meantime, with demands for high-resolution images, demands forstereographic image content, which is a new image service, have alsoincreased. A video compression technique for effectively providingstereographic image content with high resolution and ultra-highresolution is being discussed.

DISCLOSURE Technical Problem

An object of the present invention is intended to provide a method andan apparatus for efficiently performing inter prediction for anencoding/decoding target block in encoding/decoding a video signal.

An object of the present invention is intended to provide a method andan apparatus for compensating a prediction sample in consideration of achange of luminance between pictures.

An object of the present invention is intended to provide a method andan apparatus for efficiently encoding/decoding an illuminationcompensation parameter in encoding/decoding a video signal.

The technical objects to be achieved by the present invention are notlimited to the above-mentioned technical problems. And, other technicalproblems that are not mentioned will be apparently understood to thoseskilled in the art from the following description.

Technical Solution

A method and an apparatus for decoding a video signal according to thepresent invention may decode information indicating whether illuminationcompensation is performed for a current block, determine an illuminationcompensation parameter of the current block when the informationindicates that the illumination compensation is performed for thecurrent block, obtain a prediction block by performing inter predictionfor the current block, and perform the illumination compensation on thecurrent block using the illumination compensation parameter.

A method and an apparatus for encoding a video signal according to thepresent invention may obtain a prediction block by performing interprediction for a current block, determining an illumination compensationparameter for the current block, performing illumination compensationfor the prediction block using the illumination compensation parameter,and encode information indicating whether the illumination compensationis performed for the current block.

In the method and the apparatus for encoding/decoding a video signalaccording to the present invention, the illumination compensationparameter is derived based on a first template area adjacent to thecurrent block and a second template area adjacent to a reference blockincluded in a reference picture of the current block.

In the method and the apparatus for encoding/decoding a video signalaccording to the present invention, if an unavailable sample is includedin the second template area, the unavailable sample may be replaced withan available sample.

In the method and the apparatus for encoding/decoding a video signalaccording to the present invention, the available sample may be includedin the second template area or the reference block.

In the method and the apparatus for encoding/decoding a video signalaccording to the present invention, if the unavailable sample isincluded in the second template area, the unavailable sample may bereplaced with an interpolated value of a plurality of available samples.

In the method and the apparatus for encoding/decoding a video signalaccording to the present invention, obtaining the prediction block maycomprise obtaining a first prediction block based on a first referencepicture of the current block, and obtaining a second prediction blockbased on a second reference picture of the current block.

In the method and the apparatus for encoding/decoding a video signalaccording to the present invention, the illumination compensation may beperformed on at least one of the first prediction block or the secondprediction block.

In the method and the apparatus for encoding/decoding a video signalaccording to the present invention, the prediction block may be obtainedby weighted sum of the first prediction block and the second predictionblock. At this time, weights applied to the first prediction block andthe second prediction block may be determined by a weighted predictionparameter of the current block.

In the method and the apparatus for encoding/decoding a video signalaccording to the present invention, the weighted prediction parametermay be determined based on the illumination compensation parameter.

In the method and the apparatus for encoding/decoding a video signalaccording to the present invention, the prediction block may be obtainedby weighted sum of the first prediction block and the second predictionblock. At this time, a weight applied to one of the first referenceblock and the second reference block may be determined based on theillumination compensation parameter and a weight applied to the other ofthe first reference block and the second reference block may bedetermined based on a weighted prediction parameter of the currentblock.

The features briefly summarized above for the present invention are onlyillustrative aspects of the detailed description of the invention thatfollows, but do not limit the scope of the invention.

Advantageous Effects

According to the present invention, an efficient inter prediction may beperformed for an encoding/decoding target block.

According to present invention, a prediction sample may be compensatedin consideration of a change of luminance between pictures.

According to present invention, an illumination compensation parametercan be efficiently encoded/decoded.

The effects obtainable by the present invention are not limited to theabove-mentioned effects, and other effects not mentioned can be clearlyunderstood by those skilled in the art from the description below.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a device for encoding a videoaccording to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a device for decoding a videoaccording to an embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of hierarchicallypartitioning a coding block based on a tree structure according to anembodiment of the present invention.

FIG. 4 is a diagram illustrating a partition type in which binarytree-based partitioning is allowed according to an embodiment of thepresent invention.

FIG. 5 is a diagram illustrating an example in which only a binarytree-based partition of a pre-determined type is allowed according to anembodiment of the present invention.

FIG. 6 is a diagram for explaining an example in which informationrelated to the allowable number of binary tree partitioning isencoded/decoded, according to an embodiment to which the presentinvention is applied.

FIG. 7 is a diagram illustrating a partition mode applicable to a codingblock according to an embodiment of the present invention.

FIG. 8 is a flowchart illustrating processes of obtaining a residualsample according to an embodiment to which the present invention isapplied.

FIG. 9 is a flowchart illustrating an inter prediction method accordingto an embodiment to which the present invention is applied.

FIG. 10 is a diagram illustrating processes of deriving motioninformation of a current block when a merge mode is applied to thecurrent block.

FIG. 11 is a diagram illustrating processes of deriving motioninformation of a current block when an AMVP mode is applied to thecurrent block.

FIG. 12 is a flowchart of a bi-directional weighted prediction method,in accordance with an embodiment of the present invention.

FIG. 13 is a diagram for explaining a principle of bi-directionalweighted prediction.

FIG. 14 is a diagram illustrating a scan order between neighboringblocks.

FIG. 15 is a flowchart of a method of illumination compensationprediction according to the present invention.

FIG. 16 is a flowchart of a bi-directional weighted prediction methodbased on illumination compensation.

FIG. 17 is a diagram illustrating an example of performingbi-directional weighted prediction using a prediction block to whichillumination compensation is applied.

MODE FOR INVENTION

A variety of modifications may be made to the present invention andthere are various embodiments of the present invention, examples ofwhich will now be provided with reference to drawings and described indetail. However, the present invention is not limited thereto, and theexemplary embodiments can be construed as including all modifications,equivalents, or substitutes in a technical concept and a technical scopeof the present invention. The similar reference numerals refer to thesimilar element in described the drawings.

Terms used in the specification, ‘first’, ‘second’, etc. can be used todescribe various components, but the components are not to be construedas being limited to the terms. The terms are only used to differentiateone component from other components. For example, the ‘first’ componentmay be named the ‘second’ component without departing from the scope ofthe present invention, and the ‘second’ component may also be similarlynamed the ‘first’ component. The term ‘and/or’ includes a combination ofa plurality of items or any one of a plurality of terms.

It will be understood that when an element is simply referred to asbeing ‘connected to’ or ‘coupled to’ another element without being‘directly connected to’ or ‘directly coupled to’ another element in thepresent description, it may be ‘directly connected to’ or ‘directlycoupled to’ another element or be connected to or coupled to anotherelement, having the other element intervening therebetween. In contrast,it should be understood that when an element is referred to as being“directly coupled” or “directly connected” to another element, there areno intervening elements present.

The terms used in the present specification are merely used to describeparticular embodiments, and are not intended to limit the presentinvention. An expression used in the singular encompasses the expressionof the plural, unless it has a clearly different meaning in the context.In the present specification, it is to be understood that terms such as“including”, “having”, etc. are intended to indicate the existence ofthe features, numbers, steps, actions, elements, parts, or combinationsthereof disclosed in the specification, and are not intended to precludethe possibility that one or more other features, numbers, steps,actions, elements, parts, or combinations thereof may exist or may beadded.

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.Hereinafter, the same constituent elements in the drawings are denotedby the same reference numerals, and a repeated description of the sameelements will be omitted.

FIG. 1 is a block diagram illustrating a device for encoding a videoaccording to an embodiment of the present invention.

Referring to FIG. 1, the device 100 for encoding a video may include: apicture partitioning module 110, prediction modules 120 and 125, atransform module 130, a quantization module 135, a rearrangement module160, an entropy encoding module 165, an inverse quantization module 140,an inverse transform module 145, a filter module 150, and a memory 155.

The constitutional parts shown in FIG. 1 are independently shown so asto represent characteristic functions different from each other in thedevice for encoding a video. Thus, it does not mean that eachconstitutional part is constituted in a constitutional unit of separatedhardware or software. In other words, each constitutional part includeseach of enumerated constitutional parts for convenience. Thus, at leasttwo constitutional parts of each constitutional part may be combined toform one constitutional part or one constitutional part may be dividedinto a plurality of constitutional parts to perform each function. Theembodiment where each constitutional part is combined and the embodimentwhere one constitutional part is divided are also included in the scopeof the present invention, if not departing from the essence of thepresent invention.

Also, some of constituents may not be indispensable constituentsperforming essential functions of the present invention but be selectiveconstituents improving only performance thereof. The present inventionmay be implemented by including only the indispensable constitutionalparts for implementing the essence of the present invention except theconstituents used in improving performance. The structure including onlythe indispensable constituents except the selective constituents used inimproving only performance is also included in the scope of the presentinvention.

The picture partitioning module 110 may partition an input picture intoone or more processing units. Here, the processing unit may be aprediction unit (PU), a transform unit (TU), or a coding unit (CU). Thepicture partitioning module 110 may partition one picture intocombinations of multiple coding units, prediction units, and transformunits, and may encode a picture by selecting one combination of codingunits, prediction units, and transform units with a predeterminedcriterion (e.g., cost function).

For example, one picture may be partitioned into multiple coding units.A recursive tree structure, such as a quad tree structure, may be usedto partition a picture into coding units. A coding unit which ispartitioned into other coding units with one picture or a largest codingunit as a root may be partitioned with child nodes corresponding to thenumber of partitioned coding units. A coding unit which is no longerpartitioned by a predetermined limitation serves as a leaf node. Thatis, when it is assumed that only square partitioning is possible for onecoding unit, one coding unit may be partitioned into four other codingunits at most.

Hereinafter, in the embodiment of the present invention, the coding unitmay mean a unit performing encoding, or a unit performing decoding.

A prediction unit may be one of partitions partitioned into a square ora rectangular shape having the same size in a single coding unit, or aprediction unit may be one of partitions partitioned so as to have adifferent shape/size in a single coding unit.

When a prediction unit subjected to intra prediction is generated basedon a coding unit and the coding unit is not the smallest coding unit,intra prediction may be performed without partitioning the coding unitinto multiple prediction units N×N.

The prediction modules 120 and 125 may include an inter predictionmodule 120 performing inter prediction and an intra prediction module125 performing intra prediction. Whether to perform inter prediction orintra prediction for the prediction unit may be determined, and detailedinformation (e.g., an intra prediction mode, a motion vector, areference picture, etc.) according to each prediction method may bedetermined. Here, the processing unit subjected to prediction may bedifferent from the processing unit for which the prediction method anddetailed content is determined. For example, the prediction method, theprediction mode, etc. may be determined by the prediction unit, andprediction may be performed by the transform unit. A residual value(residual block) between the generated prediction block and an originalblock may be input to the transform module 130. Also, prediction modeinformation, motion vector information, etc. used for prediction may beencoded with the residual value by the entropy encoding module 165 andmay be transmitted to a device for decoding a video. When a particularencoding mode is used, it is possible to transmit to a device fordecoding video by encoding the original block as it is withoutgenerating the prediction block through the prediction modules 120 and125.

The inter prediction module 120 may predict the prediction unit based oninformation of at least one of a previous picture or a subsequentpicture of the current picture, or may predict the prediction unit basedon information of some encoded regions in the current picture, in somecases. The inter prediction module 120 may include a reference pictureinterpolation module, a motion prediction module, and a motioncompensation module.

The reference picture interpolation module may receive reference pictureinformation from the memory 155 and may generate pixel information of aninteger pixel or less then the integer pixel from the reference picture.In the case of luma pixels, an 8-tap DCT-based interpolation filterhaving different filter coefficients may be used to generate pixelinformation of an integer pixel or less than an integer pixel in unitsof a ¼ pixel. In the case of chroma signals, a 4-tap DCT-basedinterpolation filter having different filter coefficient may be used togenerate pixel information of an integer pixel or less than an integerpixel in units of a ⅛ pixel.

The motion prediction module may perform motion prediction based on thereference picture interpolated by the reference picture interpolationmodule. As methods for calculating a motion vector, various methods,such as a full search-based block matching algorithm (FBMA), a threestep search (TSS), a new three-step search algorithm (NTS), etc., may beused. The motion vector may have a motion vector value in units of a ½pixel or a ¼ pixel based on an interpolated pixel. The motion predictionmodule may predict a current prediction unit by changing the motionprediction method. As motion prediction methods, various methods, suchas a skip method, a merge method, an AMVP (Advanced Motion VectorPrediction) method, an intra block copy method, etc., may be used.

The intra prediction module 125 may generate a prediction unit based onreference pixel information neighboring to a current block which ispixel information in the current picture. When the neighboring block ofthe current prediction unit is a block subjected to inter prediction andthus a reference pixel is a pixel subjected to inter prediction, thereference pixel included in the block subjected to inter prediction maybe replaced with reference pixel information of a neighboring blocksubjected to intra prediction. That is, when a reference pixel is notavailable, at least one reference pixel of available reference pixelsmay be used instead of unavailable reference pixel information.

Prediction modes in intra prediction may include a directionalprediction mode using reference pixel information depending on aprediction direction and a non-directional prediction mode not usingdirectional information in performing prediction. A mode for predictingluma information may be different from a mode for predicting chromainformation, and in order to predict the chroma information, intraprediction mode information used to predict luma information orpredicted luma signal information may be utilized.

In performing intra prediction, when the size of the prediction unit isthe same as the size of the transform unit, intra prediction may beperformed on the prediction unit based on pixels positioned at the left,the top left, and the top of the prediction unit. However, in performingintra prediction, when the size of the prediction unit is different fromthe size of the transform unit, intra prediction may be performed usinga reference pixel based on the transform unit. Also, intra predictionusing N×N partitioning may be used for only the smallest coding unit.

In the intra prediction method, a prediction block may be generatedafter applying an AIS (Adaptive Intra Smoothing) filter to a referencepixel depending on the prediction modes. The type of the AIS filterapplied to the reference pixel may vary. In order to perform the intraprediction method, an intra prediction mode of the current predictionunit may be predicted from the intra prediction mode of the predictionunit neighboring to the current prediction unit. In prediction of theprediction mode of the current prediction unit by using mode informationpredicted from the neighboring prediction unit, when the intraprediction mode of the current prediction unit is the same as the intraprediction mode of the neighboring prediction unit, informationindicating that the prediction modes of the current prediction unit andthe neighboring prediction unit are equal to each other may betransmitted using predetermined flag information. When the predictionmode of the current prediction unit is different from the predictionmode of the neighboring prediction unit, entropy encoding may beperformed to encode prediction mode information of the current block.

Also, a residual block including information on a residual value whichis a different between the prediction unit subjected to prediction andthe original block of the prediction unit may be generated based onprediction units generated by the prediction modules 120 and 125. Thegenerated residual block may be input to the transform module 130.

The transform module 130 may transform the residual block including theinformation on the residual value between the original block and theprediction unit generated by the prediction modules 120 and 125 by usinga transform method, such as discrete cosine transform (DCT), discretesine transform (DST), and KLT. Whether to apply DCT, DST, or KLT inorder to transform the residual block may be determined based on intraprediction mode information of the prediction unit used to generate theresidual block.

The quantization module 135 may quantize values transformed to afrequency domain by the transform module 130. Quantization coefficientsmay vary depending on the block or importance of a picture. The valuescalculated by the quantization module 135 may be provided to the inversequantization module 140 and the rearrangement module 160.

The rearrangement module 160 may rearrange coefficients of quantizedresidual values.

The rearrangement module 160 may change a coefficient in the form of atwo-dimensional block into a coefficient in the form of aone-dimensional vector through a coefficient scanning method. Forexample, the rearrangement module 160 may scan from a DC coefficient toa coefficient in a high frequency domain using a zigzag scanning methodso as to change the coefficients to be in the form of one-dimensionalvectors. Depending on the size of the transform unit and the intraprediction mode, vertical direction scanning where coefficients in theform of two-dimensional blocks are scanned in the column direction orhorizontal direction scanning where coefficients in the form oftwo-dimensional blocks are scanned in the row direction may be usedinstead of zigzag scanning. That is, which scanning method among zigzagscanning, vertical direction scanning, and horizontal direction scanningis used may be determined depending on the size of the transform unitand the intra prediction mode.

The entropy encoding module 165 may perform entropy encoding based onthe values calculated by the rearrangement module 160. Entropy encodingmay use various encoding methods, for example, exponential Golombcoding, context-adaptive variable length coding (CAVLC), andcontext-adaptive binary arithmetic coding (CABAC).

The entropy encoding module 165 may encode a variety of information,such as residual value coefficient information and block typeinformation of the coding unit, prediction mode information, partitionunit information, prediction unit information, transform unitinformation, motion vector information, reference frame information,block interpolation information, filtering information, etc. from therearrangement module 160 and the prediction modules 120 and 125.

The entropy encoding module 165 may entropy encode the coefficients ofthe coding unit input from the rearrangement module 160.

The inverse quantization module 140 may inversely quantize the valuesquantized by the quantization module 135 and the inverse transformmodule 145 may inversely transform the values transformed by thetransform module 130. The residual value generated by the inversequantization module 140 and the inverse transform module 145 may becombined with the prediction unit predicted by a motion estimationmodule, a motion compensation module, and the intra prediction module ofthe prediction modules 120 and 125 such that a reconstructed block canbe generated.

The filter module 150 may include at least one of a deblocking filter,an offset correction unit, and an adaptive loop filter (ALF).

The deblocking filter may remove block distortion that occurs due toboundaries between the blocks in the reconstructed picture. In order todetermine whether to perform deblocking, the pixels included in severalrows or columns in the block may be a basis of determining whether toapply the deblocking filter to the current block. When the deblockingfilter is applied to the block, a strong filter or a weak filter may beapplied depending on required deblocking filtering strength. Also, inapplying the deblocking filter, horizontal direction filtering andvertical direction filtering may be processed in parallel.

The offset correction module may correct offset with the originalpicture in units of a pixel in the picture subjected to deblocking. Inorder to perform the offset correction on a particular picture, it ispossible to use a method of applying offset in consideration of edgeinformation of each pixel or a method of partitioning pixels of apicture into the predetermined number of regions, determining a regionto be subjected to perform offset, and applying the offset to thedetermined region.

Adaptive loop filtering (ALF) may be performed based on the valueobtained by comparing the filtered reconstructed picture and theoriginal picture. The pixels included in the picture may be divided intopredetermined groups, a filter to be applied to each of the groups maybe determined, and filtering may be individually performed for eachgroup. Information on whether to apply ALF and a luma signal may betransmitted by coding units (CU). The shape and filter coefficient of afilter for ALF may vary depending on each block. Also, the filter forALF in the same shape (fixed shape) may be applied regardless ofcharacteristics of the application target block.

The memory 155 may store the reconstructed block or picture calculatedthrough the filter module 150. The stored reconstructed block or picturemay be provided to the prediction modules 120 and 125 in performinginter prediction.

FIG. 2 is a block diagram illustrating a device for decoding a videoaccording to an embodiment of the present invention.

Referring to FIG. 2, the device 200 for decoding a video may include: anentropy decoding module 210, a rearrangement module 215, an inversequantization module 220, an inverse transform module 225, predictionmodules 230 and 235, a filter module 240, and a memory 245.

When a video bitstream is input from the device for encoding a video,the input bitstream may be decoded according to an inverse process ofthe device for encoding a video.

The entropy decoding module 210 may perform entropy decoding accordingto an inverse process of entropy encoding by the entropy encoding moduleof the device for encoding a video. For example, corresponding to themethods performed by the device for encoding a video, various methods,such as exponential Golomb coding, context-adaptive variable lengthcoding (CAVLC), and context-adaptive binary arithmetic coding (CABAC)may be applied.

The entropy decoding module 210 may decode information on intraprediction and inter prediction performed by the device for encoding avideo.

The rearrangement module 215 may perform rearrangement on the bitstreamentropy decoded by the entropy decoding module 210 based on therearrangement method used in the device for encoding a video. Therearrangement module may reconstruct and rearrange the coefficients inthe form of one-dimensional vectors to the coefficient in the form oftwo-dimensional blocks. The rearrangement module 215 may receiveinformation related to coefficient scanning performed in the device forencoding a video and may perform rearrangement via a method of inverselyscanning the coefficients based on the scanning order performed in thedevice for encoding a video.

The inverse quantization module 220 may perform inverse quantizationbased on a quantization parameter received from the device for encodinga video and the rearranged coefficients of the block.

The inverse transform module 225 may perform the inverse transform,i.e., inverse DCT, inverse DST, and inverse KLT, which is the inverseprocess of transform, i.e., DCT, DST, and KLT, performed by thetransform module on the quantization result by the device for encoding avideo. Inverse transform may be performed based on a transfer unitdetermined by the device for encoding a video. The inverse transformmodule 225 of the device for decoding a video may selectively performtransform schemes (e.g., DCT, DST, and KLT) depending on multiple piecesof information, such as the prediction method, the size of the currentblock, the prediction direction, etc.

The prediction modules 230 and 235 may generate a prediction block basedon information on prediction block generation received from the entropydecoding module 210 and previously decoded block or picture informationreceived from the memory 245.

As described above, like the operation of the device for encoding avideo, in performing intra prediction, when the size of the predictionunit is the same as the size of the transform unit, intra prediction maybe performed on the prediction unit based on the pixels positioned atthe left, the top left, and the top of the prediction unit. Inperforming intra prediction, when the size of the prediction unit isdifferent from the size of the transform unit, intra prediction may beperformed using a reference pixel based on the transform unit. Also,intra prediction using N×N partitioning may be used for only thesmallest coding unit.

The prediction modules 230 and 235 may include a prediction unitdetermination module, an inter prediction module, and an intraprediction module. The prediction unit determination module may receivea variety of information, such as prediction unit information,prediction mode information of an intra prediction method, informationon motion prediction of an inter prediction method, etc. from theentropy decoding module 210, may divide a current coding unit intoprediction units, and may determine whether inter prediction or intraprediction is performed on the prediction unit. By using informationrequired in inter prediction of the current prediction unit receivedfrom the device for encoding a video, the inter prediction module 230may perform inter prediction on the current prediction unit based oninformation of at least one of a previous picture or a subsequentpicture of the current picture including the current prediction unit.Alternatively, inter prediction may be performed based on information ofsome pre-reconstructed regions in the current picture including thecurrent prediction unit.

In order to perform inter prediction, it may be determined for thecoding unit which of a skip mode, a merge mode, an AMVP mode, and aninter block copy mode is used as the motion prediction method of theprediction unit included in the coding unit.

The intra prediction module 235 may generate a prediction block based onpixel information in the current picture. When the prediction unit is aprediction unit subjected to intra prediction, intra prediction may beperformed based on intra prediction mode information of the predictionunit received from the device for encoding a video. The intra predictionmodule 235 may include an adaptive intra smoothing (AIS) filter, areference pixel interpolation module, and a DC filter. The AIS filterperforms filtering on the reference pixel of the current block, andwhether to apply the filter may be determined depending on theprediction mode of the current prediction unit. AIS filtering may beperformed on the reference pixel of the current block by using theprediction mode of the prediction unit and AIS filter informationreceived from the device for encoding a video. When the prediction modeof the current block is a mode where AIS filtering is not performed, theAIS filter may not be applied.

When the prediction mode of the prediction unit is a prediction mode inwhich intra prediction is performed based on the pixel value obtained byinterpolating the reference pixel, the reference pixel interpolationmodule may interpolate the reference pixel to generate the referencepixel of an integer pixel or less than an integer pixel. When theprediction mode of the current prediction unit is a prediction mode inwhich a prediction block is generated without interpolation thereference pixel, the reference pixel may not be interpolated. The DCfilter may generate a prediction block through filtering when theprediction mode of the current block is a DC mode.

The reconstructed block or picture may be provided to the filter module240. The filter module 240 may include the deblocking filter, the offsetcorrection module, and the ALF.

Information on whether or not the deblocking filter is applied to thecorresponding block or picture and information on which of a strongfilter and a weak filter is applied when the deblocking filter isapplied may be received from the device for encoding a video. Thedeblocking filter of the device for decoding a video may receiveinformation on the deblocking filter from the device for encoding avideo, and may perform deblocking filtering on the corresponding block.

The offset correction module may perform offset correction on thereconstructed picture based on the type of offset correction and offsetvalue information applied to a picture in performing encoding.

The ALF may be applied to the coding unit based on information onwhether to apply the ALF, ALF coefficient information, etc. receivedfrom the device for encoding a video. The ALF information may beprovided as being included in a particular parameter set.

The memory 245 may store the reconstructed picture or block for use as areference picture or block, and may provide the reconstructed picture toan output module.

As described above, in the embodiment of the present invention, forconvenience of explanation, the coding unit is used as a termrepresenting a unit for encoding, but the coding unit may serve as aunit performing decoding as well as encoding.

In addition, a current block may represent a target block to beencoded/decoded. And, the current block may represent a coding treeblock (or a coding tree unit), a coding block (or a coding unit), atransform block (or a transform unit), a prediction block (or aprediction unit), or the like depending on an encoding/decoding step.

A picture may be encoded/decoded by divided into base blocks having asquare shape or a non-square shape. At this time, the base block may bereferred to as a coding tree unit. The coding tree unit may be definedas a coding unit of the largest size allowed within a sequence or aslice. Information regarding whether the coding tree unit has a squareshape or has a non-square shape or information regarding a size of thecoding tree unit may be signaled through a sequence parameter set, apicture parameter set, or a slice header. The coding tree unit may bedivided into smaller size partitions. At this time, if it is assumedthat a depth of a partition generated by dividing the coding tree unitis 1, a depth of a partition generated by dividing the partition havingdepth 1 may be defined as 2. That is, a partition generated by dividinga partition having a depth k in the coding tree unit may be defined ashaving a depth k+1.

A partition of arbitrary size generated by dividing a coding tree unitmay be defined as a coding unit. The coding unit may be recursivelydivided or divided into base units for performing prediction,quantization, transform, or in-loop filtering, and the like. Forexample, a partition of arbitrary size generated by dividing the codingunit may be defined as a coding unit, or may be defined as a transformunit or a prediction unit, which is a base unit for performingprediction, quantization, transform or in-loop filtering and the like.

Partitioning of a coding tree unit or a coding unit may be performedbased on at least one of a vertical line and a horizontal line. Inaddition, the number of vertical lines or horizontal lines partitioningthe coding tree unit or the coding unit may be at least one or more. Forexample, the coding tree unit or the coding unit may be divided into twopartitions using one vertical line or one horizontal line, or the codingtree unit or the coding unit may be divided into three partitions usingtwo vertical lines or two horizontal lines. Alternatively, the codingtree unit or the coding unit may be partitioned into four partitionshaving a length and a width of ½ by using one vertical line and onehorizontal line.

When a coding tree unit or a coding unit is divided into a plurality ofpartitions using at least one vertical line or at least one horizontalline, the partitions may have a uniform size or a different size.Alternatively, any one partition may have a different size from theremaining partitions.

In the embodiments described below, it is assumed that a coding treeunit or a coding unit is divided into a quad tree structure or a binarytree structure. However, it is also possible to divide a coding treeunit or a coding unit using a larger number of vertical lines or alarger number of horizontal lines.

FIG. 3 is a diagram illustrating an example of hierarchicallypartitioning a coding block based on a tree structure according to anembodiment of the present invention.

An input video signal is decoded in predetermined block units. Such adefault unit for decoding the input video signal is a coding block. Thecoding block may be a unit performing intra/inter prediction, transform,and quantization. In addition, a prediction mode (e.g., intra predictionmode or inter prediction mode) is determined in units of a coding block,and the prediction blocks included in the coding block may share thedetermined prediction mode. The coding block may be a square ornon-square block having an arbitrary size in a range of 8×8 to 64×64, ormay be a square or non-square block having a size of 128×128, 256×256,or more.

Specifically, the coding block may be hierarchically partitioned basedon at least one of a quad tree and a binary tree. Here, quad tree-basedpartitioning may mean that a 2N×2N coding block is partitioned into fourN×N coding blocks, and binary tree-based partitioning may mean that onecoding block is partitioned into two coding blocks. Even if the binarytree-based partitioning is performed, a square-shaped coding block mayexist in the lower depth.

Binary tree-based partitioning may be symmetrically or asymmetricallyperformed. The coding block partitioned based on the binary tree may bea square block or a non-square block, such as a rectangular shape. Forexample, a partition type in which the binary tree-based partitioning isallowed may comprise at least one of a symmetric type of 2N×N(horizontal directional non-square coding unit) or N×2N (verticaldirection non-square coding unit), asymmetric type of nL×2N, nR×2N,2N×nU, or 2N×nD.

Binary tree-based partitioning may be limitedly allowed to one of asymmetric or an asymmetric type partition. In this case, constructingthe coding tree unit with square blocks may correspond to quad tree CUpartitioning, and constructing the coding tree unit with symmetricnon-square blocks may correspond to binary tree partitioning.Constructing the coding tree unit with square blocks and symmetricnon-square blocks may correspond to quad and binary tree CUpartitioning.

Binary tree-based partitioning may be performed on a coding block wherequad tree-based partitioning is no longer performed. Quad tree-basedpartitioning may no longer be performed on the coding block partitionedbased on the binary tree.

Furthermore, partitioning of a lower depth may be determined dependingon a partition type of an upper depth. For example, if binary tree-basedpartitioning is allowed in two or more depths, only the same type as thebinary tree partitioning of the upper depth may be allowed in the lowerdepth. For example, if the binary tree-based partitioning in the upperdepth is performed with 2N×N type, the binary tree-based partitioning inthe lower depth is also performed with 2N×N type. Alternatively, if thebinary tree-based partitioning in the upper depth is performed with N×2Ntype, the binary tree-based partitioning in the lower depth is alsoperformed with N×2N type.

On the contrary, it is also possible to allow, in a lower depth, only atype different from a binary tree partitioning type of a upper depth.

It may be possible to limit only a specific type of binary tree basedpartitioning to be used for sequence, slice, coding tree unit, or codingunit. As an example, only 2N×N type or N×2N type of binary tree-basedpartitioning may be allowed for the coding tree unit. An availablepartition type may be predefined in an encoder or a decoder. Orinformation on available partition type or on unavailable partition typeon may be encoded and then signaled through a bitstream.

FIG. 5 is a diagram illustrating an example in which only a specifictype of binary tree-based partitioning is allowed. FIG. 5A shows anexample in which only N×2N type of binary tree-based partitioning isallowed, and FIG. 5B shows an example in which only 2N×N type of binarytree-based partitioning is allowed. In order to implement adaptivepartitioning based on the quad tree or binary tree, informationindicating quad tree-based partitioning, information on the size/depthof the coding block that quad tree-based partitioning is allowed,information indicating binary tree-based partitioning, information onthe size/depth of the coding block that binary tree-based partitioningis allowed, information on the size/depth of the coding block thatbinary tree-based partitioning is not allowed, information on whetherbinary tree-based partitioning is performed in a vertical direction or ahorizontal direction, etc. may be used.

In addition, information on the number of times a binary treepartitioning is allowed, a depth at which the binary tree partitioningis allowed, or the number of the depths at which the binary treepartitioning is allowed may be obtained for a coding tree unit or aspecific coding unit. The information may be encoded in units of acoding tree unit or a coding unit, and may be transmitted to a decoderthrough a bitstream.

For example, a syntax ‘max_binary_depth_idx_minus1’ indicating a maximumdepth at which binary tree partitioning is allowed may beencoded/decoded through a bitstream. In this case,max_binary_depth_idx_minus1+1 may indicate the maximum depth at whichthe binary tree partitioning is allowed.

Referring to the example shown in FIG. 6, in FIG. 6, the binary treepartitioning has been performed for a coding unit having a depth of 2and a coding unit having a depth of 3. Accordingly, at least one ofinformation indicating the number of times the binary tree partitioningin the coding tree unit has been performed (i.e., 2 times), informationindicating the maximum depth which the binary tree partitioning has beenallowed in the coding tree unit (i.e., depth 3), or the number of depthsin which the binary tree partitioning has been performed in the codingtree unit (i.e., 2 (depth 2 and depth 3)) may be encoded/decoded througha bitstream.

As another example, at least one of information on the number of timesthe binary tree partitioning is permitted, the depth at which the binarytree partitioning is allowed, or the number of the depths at which thebinary tree partitioning is allowed may be obtained for each sequence oreach slice. For example, the information may be encoded in units of asequence, a picture, or a slice unit and transmitted through abitstream. Accordingly, at least one of the number of the binary treepartitioning in a first slice, the maximum depth in which the binarytree partitioning is allowed in the first slice, or the number of depthsin which the binary tree partitioning is performed in the first slicemay be difference from a second slice. For example, in the first slice,binary tree partitioning may be permitted for only one depth, while inthe second slice, binary tree partitioning may be permitted for twodepths.

As another example, the number of times the binary tree partitioning ispermitted, the depth at which the binary tree partitioning is allowed,or the number of depths at which the binary tree partitioning is allowedmay be set differently according to a time level identifier (TemporalID)of a slice or a picture. Here, the temporal level identifier(TemporalID) is used to identify each of a plurality of layers of videohaving a scalability of at least one of view, spatial, temporal orquality.

As shown in FIG. 3, the first coding block 300 with the partition depth(split depth) of k may be partitioned into multiple second coding blocksbased on the quad tree. For example, the second coding blocks 310 to 340may be square blocks having the half width and the half height of thefirst coding block, and the partition depth of the second coding blockmay be increased to k+1.

The second coding block 310 with the partition depth of k+1 may bepartitioned into multiple third coding blocks with the partition depthof k+2. Partitioning of the second coding block 310 may be performed byselectively using one of the quad tree and the binary tree depending ona partitioning method. Here, the partitioning method may be determinedbased on at least one of the information indicating quad tree-basedpartitioning and the information indicating binary tree-basedpartitioning.

When the second coding block 310 is partitioned based on the quad tree,the second coding block 310 may be partitioned into four third codingblocks 310 a having the half width and the half height of the secondcoding block, and the partition depth of the third coding block 310 amay be increased to k+2. In contrast, when the second coding block 310is partitioned based on the binary tree, the second coding block 310 maybe partitioned into two third coding blocks. Here, each of two thirdcoding blocks may be a non-square block having one of the half width andthe half height of the second coding block, and the partition depth maybe increased to k+2. The second coding block may be determined as anon-square block of a horizontal direction or a vertical directiondepending on a partitioning direction, and the partitioning directionmay be determined based on the information on whether binary tree-basedpartitioning is performed in a vertical direction or a horizontaldirection.

In the meantime, the second coding block 310 may be determined as a leafcoding block that is no longer partitioned based on the quad tree or thebinary tree. In this case, the leaf coding block may be used as aprediction block or a transform block.

Like partitioning of the second coding block 310, the third coding block310 a may be determined as a leaf coding block, or may be furtherpartitioned based on the quad tree or the binary tree.

In the meantime, the third coding block 310 b partitioned based on thebinary tree may be further partitioned into coding blocks 310 b-2 of avertical direction or coding blocks 310 b-3 of a horizontal directionbased on the binary tree, and the partition depth of the relevant codingblocks may be increased to k+3. Alternatively, the third coding block310 b may be determined as a leaf coding block 310 b-1 that is no longerpartitioned based on the binary tree. In this case, the coding block 310b-1 may be used as a prediction block or a transform block. However, theabove partitioning process may be limitedly performed based on at leastone of the information on the size/depth of the coding block that quadtree-based partitioning is allowed, the information on the size/depth ofthe coding block that binary tree-based partitioning is allowed, and theinformation on the size/depth of the coding block that binary tree-basedpartitioning is not allowed.

A number of a candidate that represent a size of a coding block may belimited to a predetermined number, or a size of a coding block in apredetermined unit may have a fixed value. As an example, the size ofthe coding block in a sequence or in a picture may be limited to have256×256, 128×128, or 32×32. Information indicating the size of thecoding block in the sequence or in the picture may be signaled through asequence header or a picture header.

As a result of partitioning based on a quad tree and a binary tree, acoding unit may be represented as square or rectangular shape of anarbitrary size.

A coding block is encoded using at least one of a skip mode, intraprediction, inter prediction, or a skip method. Once a coding block isdetermined, a prediction block may be determined through predictivepartitioning of the coding block. The predictive partitioning of thecoding block may be performed by a partition mode (Part mode) indicatinga partition type of the coding block. A size or a shape of theprediction block may be determined according to the partition mode ofthe coding block. For example, a size of a prediction block determinedaccording to the partition mode may be equal to or smaller than a sizeof a coding block.

FIG. 7 is a diagram illustrating a partition mode that may be applied toa coding block when the coding block is encoded by inter prediction.

When a coding block is encoded by inter prediction, one of 8partitioning modes may be applied to the coding block, as in the exampleshown in FIG. 4.

When a coding block is encoded by intra prediction, a partition modePART 2N×2N or a partition mode PART_N×N may be applied to the codingblock.

PART_N×N may be applied when a coding block has a minimum size. Here,the minimum size of the coding block may be predefined in an encoder anda decoder. Or, information regarding the minimum size of the codingblock may be signaled via a bitstream. For example, the minimum size ofthe coding block may be signaled through a slice header, so that theminimum size of the coding block may be defined per slice.

In general, a prediction block may have a size from 64×64 to 4×4.However, when a coding block is encoded by inter prediction, it may berestricted that the prediction block does not have a 4×4 size in orderto reduce memory bandwidth when performing motion compensation.

FIG. 8 is a flowchart illustrating processes of obtaining a residualsample according to an embodiment to which the present invention isapplied.

First, a residual coefficient of a current block may be obtained S810. Adecoder may obtain a residual coefficient through a coefficient scanningmethod. For example, the decoder may perform a coefficient scan using ajig-zag scan, a vertical scan, or a horizontal scan, and may obtainresidual coefficients in a form of a two-dimensional block.

An inverse quantization may be performed on the residual coefficient ofthe current block S820.

An inverse transform is selectively performed according to whether toskip the inverse transform on the dequantized residual coefficient ofthe current block S830. Specifically, the decoder may determine whetherto skip the inverse transform on at least one of a horizontal directionor a vertical direction of the current block. When it is determined toapply the inverse transform on at least one of the horizontal directionor the vertical direction of the current block, a residual sample of thecurrent block may be obtained by inverse transforming the dequantizedresidual coefficient of the current block. Here, the inverse transformcan be performed using at least one of DCT, DST, and KLT.

When the inverse transform is skipped in both the horizontal directionand the vertical direction of the current block, inverse transform isnot performed in the horizontal direction and the vertical direction ofthe current block. In this case, the residual sample of the currentblock may be obtained by scaling the dequantized residual coefficientwith a predetermined value.

Skipping the inverse transform on the horizontal direction means thatthe inverse transform is not performed on the horizontal direction butthe inverse transform is performed on the vertical direction. At thistime, scaling may be performed in the horizontal direction.

Skipping the inverse transform on the vertical direction means that theinverse transform is not performed on the vertical direction but theinverse transform is performed on the horizontal direction. At thistime, scaling may be performed in the vertical direction.

It may be determined whether or not an inverse transform skip techniquemay be used for the current block depending on a partition type of thecurrent block. For example, if the current block is generated through abinary tree-based partitioning, the inverse transform skip scheme may berestricted for the current block. Accordingly, when the current block isgenerated through the binary tree-based partitioning, the residualsample of the current block may be obtained by inverse transforming thecurrent block. In addition, when the current block is generated throughbinary tree-based partitioning, encoding/decoding of informationindicating whether or not the inverse transform is skipped (e.g.,transform_skip_flag) may be omitted.

Alternatively, when the current block is generated through binarytree-based partitioning, it is possible to limit the inverse transformskip scheme to at least one of the horizontal direction or the verticaldirection. Here, the direction in which the inverse transform skipscheme is limited may be determined based on information decoded fromthe bitstream, or may be adaptively determined based on at least one ofa size of the current block, a shape of the current block, or an intraprediction mode of the current block.

For example, when the current block is a non-square block having a widthgreater than a height, the inverse transform skip scheme may be allowedonly in the vertical direction and restricted in the horizontaldirection. That is, when the current block is 2N×N, the inversetransform is performed in the horizontal direction of the current block,and the inverse transform may be selectively performed in the verticaldirection.

On the other hand, when the current block is a non-square block having aheight greater than a width, the inverse transform skip scheme may beallowed only in the horizontal direction and restricted in the verticaldirection. That is, when the current block is N×2N, the inversetransform is performed in the vertical direction of the current block,and the inverse transform may be selectively performed in the horizontaldirection.

In contrast to the above example, when the current block is a non-squareblock having a width greater than a height, the inverse transform skipscheme may be allowed only in the horizontal direction, and when thecurrent block is a non-square block having a height greater than awidth, the inverse transform skip scheme may be allowed only in thevertical direction.

Information indicating whether or not to skip the inverse transform withrespect to the horizontal direction or information indicating whether toskip the inverse transformation with respect to the vertical directionmay be signaled through a bitstream. For example, the informationindicating whether or not to skip the inverse transform on thehorizontal direction is a 1-bit flag, ‘hor_transform_skip_flag’, andinformation indicating whether to skip the inverse transform on thevertical direction is a 1-bit flag, ‘ver_transform_skip_flag’. Theencoder may encode at least one of ‘hor_transform_skip_flag’ or‘ver_transform_skip_flag’ according to the shape of the current block.Further, the decoder may determine whether or not the inverse transformon the horizontal direction or on the vertical direction is skipped byusing at least one of “hor_transform_skip_flag” or“ver_transform_skip_flag”.

It may be set to skip the inverse transform for any one direction of thecurrent block depending on a partition type of the current block. Forexample, if the current block is generated through a binary tree-basedpartitioning, the inverse transform on the horizontal direction orvertical direction may be skipped. That is, if the current block isgenerated by binary tree-based partitioning, it may be determined thatthe inverse transform for the current block is skipped on at least oneof a horizontal direction or a vertical direction withoutencoding/decoding information (e.g., transform_skip_flag,hor_transform_skip_flag, ver_transform_skip_flag) indicating whether ornot the inverse transform of the current block is skipped.

FIG. 9 is a flowchart illustrating an inter prediction method accordingto an embodiment to which the present invention is applied.

Referring to FIG. 9, motion information of a current block is determinedS910. The motion information of the current block may include at leastone of a motion vector relating to the current block, a referencepicture index of the current block, or an inter prediction direction ofthe current block.

The motion information of the current block may be obtained based on atleast one of information signaled through a bitstream or motioninformation of a neighboring block adjacent to the current block.

FIG. 10 is a diagram illustrating processes of deriving motioninformation of a current block when a merge mode is applied to thecurrent block.

If the merge mode is applied to the current block, a spatial mergecandidate may be derived from a spatial neighboring block of the currentblock S1010. The spatial neighboring block may comprise at least one ofblocks adjacent to a left, a top or a corner (e.g., at least one of atop-left corner, a right-top corner or a left-bottom corner) of thecurrent block.

Motion information of the spatial merge candidate may be set to be thesame as motion information of the spatial neighboring block.

A temporal merge candidate may be derived from a temporal neighboringblock of the current block 51020. The temporal neighboring block maymean a block included in a collocated picture. The collocated picturehas a picture order count (POC) different from a current pictureincluding the current block. The collocated picture may be determined asa picture having a predefined index in a reference picture list or maybe determined by an index signaled from a bitstream. The temporalneighboring block may be determined to be a block comprising coordinatesin a collocated block that has the same position as the current block inthe collocated picture, or a block adjacent to the collocated block. Forexample, at least one of a block including center coordinates of thecollocated block or a block adjacent to the bottom left boundary of thecollocated block may be determined as the temporal neighboring block.

Motion information of the temporal merge candidate may be determinedbased on motion information of the temporal neighboring block. Forexample, a motion vector of the temporal merge candidate may bedetermined based on a motion vector of the temporal neighboring block.In addition, an inter prediction direction of the temporal mergecandidate may be set to be the same as an inter prediction direction ofthe temporal neighboring block. However, a reference picture index ofthe temporal merge candidate may have a fixed value. For example, thereference picture index of the temporal merge candidate may be set to‘0’.

Thereafter, a merge candidate list including the spatial merge candidateand the temporal merge candidate may be generated 51030. If the numberof merge candidates included in the merge candidate list is smaller thana maximum merge candidate number, a combined merge candidate combiningtwo or more merge candidates may be included in the merge candidatelist.

When the merge candidate list is generated, at least one of mergecandidates included in the merge candidate list may be specified basedon a merge candidate index S1040.

Motion information of the current block may be set to be the same asmotion information of the merge candidate specified by the mergecandidate index S1050. For example, when the spatial merge candidate isselected by the merge candidate index, the motion information of thecurrent block may be set to be the same as the motion information of thespatial neighboring block. Alternatively, when the temporal mergecandidate is selected by the merge candidate index, the motioninformation of the current block may be set to be the same as the motioninformation of the temporal neighboring block.

FIG. 11 is a diagram illustrating processes of deriving motioninformation of a current block when an AMVP mode is applied to thecurrent block.

When the AMVP mode is applied to the current block, at least one of aninter prediction direction of the current block or a reference pictureindex may be decoded from a bitstream S1110. That is, when the AMVP modeis applied, at least one of the inter prediction direction or thereference picture index of the current block may be determined based oninformation encoded through the bitstream.

A spatial motion vector candidate may be determined based on a motionvector of a spatial neighboring block of the current block S1120. Thespatial motion vector candidate may include at least one of a firstspatial motion vector candidate derived from a top neighboring block ofthe current block and a second spatial motion vector candidate derivedfrom a left neighboring block of the current block. Here, the topneighboring block may include at least one of blocks adjacent to a topor a top right corner of the current block, and the left neighboringblock of the current block may include at least one of blocks adjacentto a left or a bottom left corner of the current block. A block adjacentto a top left corner of the current block may be treated as the topneighboring block, or as the left neighboring block.

When reference pictures between the current block and the spatialneighboring block are different from each other, it is also possible toobtain the spatial motion vector by scaling the motion vector of thespatial neighboring block.

A temporal motion vector candidate may be determined based on a motionvector of a temporal neighboring block of the current block S1130. Whenreference pictures between the current block and the temporalneighboring block are different from each other, it is also possible toobtain the temporal motion vector by scaling the motion vector of thetemporal neighboring block.

A motion vector candidate list including the spatial motion vectorcandidate and the temporal motion vector candidate may be generatedS1140.

When the motion vector candidate list is generated, at least one ofmotion vector candidates included in the motion vector candidate listmay be specified based on information specifying at least one from themotion vector candidate list S1150.

The motion vector candidate specified by the information may be set as amotion vector prediction value of the current block, and a motion vectordifference value may be added to the motion vector prediction value toobtain a motion vector of the current block S1160. At this time, themotion vector difference value may be parsed through the bitstream.

When motion information of the current block is obtained, motioncompensation for the current block may be performed based on theobtained motion information S920. More specifically, the motioncompensation for the current block may be performed based on the interprediction direction, the reference picture index, and the motion vectorof the current block.

The inter prediction direction may indicate N directions. Here, N is anatural number, and may be 1, 2, or 3 or more. If the inter predictiondirection indicates N directions, it means that inter prediction of thecurrent block is performed based on N reference pictures or N referenceblocks. For example, when the inter prediction direction of the currentblock indicates a uni-direction, the inter prediction of the currentblock may be performed based on one reference picture. On the otherhands, when the inter prediction of the current block indicates abi-direction, the inter prediction of the current block may be performedusing two reference pictures or two reference blocks.

It is also possible to determine whether a multi-directional predictionis allowed for the current block based on at least one of a size or ashape of the current block. For example, when a coding unit has a squareshape, the multi-directional prediction is allowed for encoding/decodingthereof. On the other hand, when the coding unit has a non-square shape,only uni-directional prediction is allowed for encoding/decodingthereof. On the contrary to the cases above, it is also possible to setthat the multi-directional prediction is allowed for encoding/decodingthe coding unit when it has the non-square shape, and only theuni-directional prediction is allowed for encoding/decoding the codingunit when it has the square shape. Alternatively, it is also possible toset that the multi-directional prediction is not allowed forencoding/decoding a prediction unit, when the prediction unit has thenon-square shape of 4×8 or 8×4 or the like.

The reference picture index may specify a reference picture to be usedfor inter prediction of the current block. Specifically, the referencepicture index may specify any one of reference pictures included in thereference picture list. For example, when the inter prediction directionof the current block is bi-directional, the reference picture (referencepicture L0) included in the reference picture list L0 is specified by areference picture index L0, and the reference picture (reference pictureL1) included in the reference picture list L1 is specified by areference picture index L1.

Alternatively, one reference picture may be included in two or morereference picture lists. Accordingly, even if the reference pictureindex of the reference picture included in the reference picture list L0and the reference picture index of the reference picture included in thereference picture list L1 are different, temporal orders (picture ordercount, POC) of both reference pictures may be the same.

The motion vector may be used to specify a position of a referenceblock, in the reference picture, corresponding to a prediction block ofthe current block. Inter prediction of the current block may beperformed based on the reference block, specified by the motion vector,in the reference picture. For example, an integer pixel included in thereference block or a non-integer pixel generated by interpolatinginteger pixels may be generated as a prediction sample of the currentblock. It is also possible that reference blocks specified by differentmotion vectors may be included in the same reference picture. Forexample, when the reference picture selected from the reference picturelist L0 and the reference picture selected from the reference picturelist L1 are the same, the reference block specified by a motion vectorL0 and the reference block specified by a motion vector L1 may beincluded in the same reference picture.

As described above, when the inter prediction direction of the currentblock indicates two or more directions, the motion compensation for thecurrent block may be performed based on two or more reference picturesor two or more reference blocks.

For example, when the current block is encoded with bi-directionalprediction, the prediction block of the current block may be obtainedbased on two reference blocks obtained from two reference pictures.Also, when the current block is encoded with bi-directional prediction,a residual block indicating the difference between an original block andthe prediction block obtained based on the two reference blocks may beencoded/decoded.

When two or more reference pictures are used, the motion compensationfor the current block may be performed by applying the same or differentweights to the respective reference pictures. Hereinafter, a method ofperforming weighted prediction on the current block will be described indetail in the following embodiments when the inter prediction directionindicates two or more directions. For convenience of explanation, it isassumed that the inter prediction direction of the current block isbi-directional. However, even when the inter prediction direction of thecurrent block indicates three or more, the following embodiment can beapplied with application. In addition, the motion compensation for thecurrent block using two prediction images will be referred to as abi-directional prediction method or a bi-directional predictionencoding/decoding method.

When the bi-directional prediction is applied to the current block,reference pictures used for the bi-directional prediction of the currentblock may include a picture whose temporal order (Picture Order Count,POC) is previous to the current picture, a picture whose temporal orderis subsequent to the current picture, or the current picture. Forexample, one of two reference pictures may be a picture whose temporalorder is previous to the current picture, and the other picture may be apicture whose temporal order is subsequent to the current picture.Alternatively, one of the two reference pictures may be the currentpicture, and the other picture may be a picture whose temporal order isprevious to the current block or whose temporal order is subsequent tothe current picture. Alternatively, both of the two reference picturesmay have temporal orders previous to the current picture, or may havetemporal orders subsequent to the current picture. Alternatively, bothof the two reference pictures may be the current picture.

Two prediction blocks may be generated from each of two referencepicture lists. For example, a prediction block based on the referencepicture L0 may be generated based on the motion vector L0, and aprediction block based on the reference picture L1 may be generatedbased on the motion vector L1. It is also possible that the predictionblock generated by the motion vector L0 and the prediction blockgenerated by the motion vector L1 may be generated based on the samereference picture.

A prediction block of the current block may be obtained based on anaverage value of the prediction blocks generated based on both referencepictures. For example, Equation 1 shows an example of obtaining theprediction block of the current block based on the average value of aplurality of the prediction blocks.P(x)=½*P ₀(x)+½*P ₁(x)  [Equation 1]

In Equation 1, P(x) denotes a final prediction sample of the currentblock or a bi-directionally predicted prediction sample, and P_(N)(x)denotes a sample value of a prediction block LN generated based on areference picture LN. For example, P₀(x) may mean a prediction sample ofthe prediction block generated based on the reference picture L0, andP₁(x) may mean a prediction sample of the prediction block generatedbased on the reference picture L1. That is, according to Equation 1, thefinal prediction block of the current block may be obtained based on theweighted sum of the plurality of the prediction blocks generated basedon the plurality of the reference pictures. At this time, a weight of afixed value predefined in the encoder/decoder may be assigned to eachprediction block.

According to an embodiment of the present invention, the finalprediction block of the current block is obtained based on the weightedsum of a plurality of the prediction blocks, and the weight assigned toeach prediction block may be variably/adaptively determined. Forexample, when both reference pictures or both prediction blocks havedifferent brightness, it is more effective to perform bi-directionalprediction for the current block by applying different weights to eachof the prediction blocks than to perform the bi-directional predictionfor the current block by averaging the prediction blocks. Hereinafter,for convenience of explanation, the bi-directional prediction methodwhen the weight assigned to each of the prediction blocks isvariably/adaptively determined will be referred to as ‘bi-directionalweighted prediction’.

It is also possible to determine whether or not the bi-directionalweighted prediction is allowed for the current block based on at leastone of a size or a shape of the current block. For example, if thecoding unit has a square shape, it is allowed to encode/decode thereofusing the bi-directional weighted prediction, whereas if the coding unithas a non-square shape, it is not allowed to encode/decode thereof usingthe bi-directional weighted prediction. On the contrary to the abovecases, it is also possible to set that it is allowed to encode/decodethe coding block using the bi-directional weighted prediction when ithas the non-square shape, and it is not allowed to encode/decode thecoding block using the bi-directional weighted prediction when it hasthe square shape. Alternatively, it is also possible to set that thebi-directional weighted prediction is not allowed for encoding/decodingthe prediction unit when the prediction unit is a non-square partitionhaving a size of 4×8 or 8×4 or the like.

FIG. 12 is a flowchart of a bi-directional weighted prediction method,in accordance with an embodiment of the present invention.

In order to perform the bi-directional weighted prediction, a weightedprediction parameter for the current block may be determined S1210. Theweighted prediction parameter may be used to determine a weight to beapplied to both reference pictures. For example, as depicted in FIG. 13,a weight of 1-w may be applied to a prediction block generated based ona reference picture L0, and a weight of w may be applied to a predictionblock generated based on a reference picture L1. Based on the weightedprediction parameters, the weight to be applied to each prediction blockis determined S1220, and a weighted sum operation of a plurality of theprediction blocks is performed based on the determined weight togenerate a final predicted block of the current block S1230. Forexample, the final prediction block of the current block may begenerated based on the following Equation 2.P(x)=(1−w)*P ₀(x)+w*P ₁(x)  [Equation 2]

In Equation 2, w represents the weighted prediction parameter.

As shown in Equation 2, the final prediction block P(x) of the currentblock may be obtained by assigning the weight of 1-w to the predictionblock P₀ and assigning the weight of w to the prediction block P₁. It isalso possible to assign the weight of w to the prediction block P₀ andto assign the weight of 1-w to the prediction block P₁, as opposed tothat shown in Equation 2.

The weighted prediction parameter may be determined based on adifference of brightness between the reference pictures, or may bedetermined based on a distance between the current picture and thereference pictures (i.e., the POC difference). Alternatively, it is alsopossible to determine the weighted prediction parameter based on thesize or the shape of the current block.

The weighted prediction parameter may be determined in units of a block(for example, a coding tree unit, a coding unit, a prediction unit, or atransform unit), or may be determined in units of a slice or a picture.

At this time, the weighted prediction parameter may be determined basedon predefined candidate weighted prediction parameters. As an example,the weighted prediction parameter may be determined to be one ofpredefined values like −¼, ¼, ⅜, ½, ⅝, ¾ or 5/4.

Alternatively, after determining a weighted prediction parameter set forthe current block, it is also possible to determine the weightedprediction parameter from at least one of candidate weighted predictionparameters included in the determined weighted prediction parameter set.The weighted prediction parameter set may be determined in units of ablock (for example, a coding tree unit, a coding unit, a predictionunit, or a transform unit), or may be determined in units of a slice ora picture.

For example, if one of weighted prediction parameter sets w0 and w1 isselected, at least one of candidate weighted prediction parametersincluded in the selected weighted prediction parameter set may bedetermined as the weighted prediction parameter for the current block.For example, it is assumed as ‘w0={−¼, ¼, ⅜, ½, ⅝, ¾, 5/4}’ and ‘w1={−⅜,4, ⅜, ½, ⅝, ¾}’. When the weighted prediction parameter set w0 isselected, the weighted prediction parameter w of the current block maybe determined as one of the candidate weighted prediction parameters −¼,¼, ⅜, ½, ⅝, ¾ and 5/4 included in the w0.

The weighted prediction parameter set available for the current blockmay be determined according to a temporal order or a temporal directionof the reference picture used for the bi-directional prediction. Thetemporal order may indicate an encoding/decoding order between pictures,or may indicate an output order (e.g., POC) of the pictures. Inaddition, the temporal direction may indicate whether the temporal orderof the reference picture is previous to or subsequent to the currentpicture.

As an example, depending on whether two reference pictures used for thebi-directional prediction have the same temporal order, the weightedprediction parameter set available to the current picture may bedetermined. For example, depending on whether the reference picture L0and the reference picture L1 are the same picture (that is, the temporalorder of the pictures being same) or whether the reference picture L0and the reference picture L1 are different from each other (that is,temporal orders of the pictures being different), the weightedprediction parameter set available for the current block may be variablydetermined.

Different weighted prediction parameter sets may mean that at least oneof an absolute value, a sign, or a number of weighted predictionparameters included in each set of weighted prediction parameters aredifferent. For example, when the temporal directions of the referencepicture L0 and the reference picture L1 are the same, the weightedprediction parameter set w0={−¼, ¼, ⅜, ½, ⅝, 5/4} may be used, and whenthe temporal directions of the reference picture L0 and the referencepicture L1 are different, the weighted prediction parameters set w1={−⅜,−¼, ¼, ⅜, ½, /8, ¾} may be used.

As an example, depending on whether or not the temporal directions ofthe two reference pictures used in the bi-directional prediction are thesame, the weighted prediction parameter set available for the currentpicture may be determined. For example, the weighted predictionparameter set available for the current block may be determineddifferently between when the temporal directions of the two referencepictures are the same and when the temporal directions of the tworeference pictures are different. Specifically, the weighted predictionparameter of the current block may be determined differently accordingto whether or not both the reference picture L0 and the referencepicture L1 are previous to the current picture, whether or not both thereference picture L0 and the reference picture L1 are subsequent to thecurrent picture, or whether or not the temporal directions of thereference picture L0 and the reference picture L1 are different.

The number of available candidate weighted prediction parameters or thenumber of available weighted prediction parameter sets may be setdifferently for each block, each slice or each picture. For example, thenumber of available candidate weighted prediction parameters or thenumber of available weighted prediction parameter sets may be signaledin units of a slice. Accordingly, the number of available candidateweighted prediction parameters or the number of available weightedprediction parameter sets may be different for each slice.

The weighted prediction parameter may be derived from a neighboringblock adjacent to the current block. Here, the neighboring blockadjacent to the current block may include at least one of a spatialneighboring block or a temporal neighboring block of the current block.

As an example, the weighted prediction parameter of the current blockmay be set to a minimum value or a maximum value among weightedprediction parameters of neighboring blocks adjacent to the currentblock, or may be set to an average value of weighted predictionparameters of neighboring blocks.

As an example, the weighted prediction parameter of the current blockmay be derived from a neighboring block located at a predeterminedposition among neighboring blocks adjacent to the current block. Here,the predetermined position may be determined variably or fixedly.Specifically, the position of the neighboring block is determined by asize of the current block (e.g., a coding unit, a prediction unit or atransform unit), a position of the current block in the coding treeunit, a shape of the current block (e.g., a partition type of thecurrent block), or a partition index of the current block.Alternatively, the position of the neighboring block may be predefinedin the encoder/decoder and fixedly determined.

As an example, the weighted prediction parameter of the current blockmay be derived from a neighboring block to which the bi-directionalweighted prediction is applied among neighboring blocks adjacent to thecurrent block. Specifically, the weighted prediction parameter of thecurrent block may be derived from a weighted prediction parameter of afirst detected neighboring block to which the bi-directional weightedprediction is applied when the neighboring blocks adjacent to thecurrent block is scanned in a predetermined order. FIG. 14 is a diagramillustrating a scan order between neighboring blocks. In FIG. 14, thescan is performed in order of a left neighboring block, an upperneighboring block, an upper right neighboring block, a lower leftneighboring block, and a left upper neighboring block, but the presentinvention is not limited to the illustrated example. When the scan isperformed following the predefined order, the weighted predictionparameter of the first detected neighboring block to which thebi-directional weighted prediction may be used as the weightedprediction parameter of the current block.

Alternatively, when the scan is performed following the predefinedorder, it is also possible to set the weighted prediction parameter ofthe first detected neighboring block to which the weightedbi-directional prediction is applied as the weighted predictionparameter prediction value of the current block. In this case, theweighted prediction parameter of the current block may be obtained byusing the weighted prediction parameter prediction value and theweighted prediction parameter residual value.

As an example, it is also possible to derive the weighted predictionparameter of the current block from a spatial or a temporal neighboringblock merged with motion information of the current block, or from aspatial or a temporal neighboring block used to derive a motion vectorprediction value of the current block.

It is also possible to signal information for determining the weightedprediction parameter through a bitstream. For example, the weightedprediction parameter of the current block may be determined based on atleast one of information indicating a value of the weighted predictionparameter, index information specifying one of candidate weightedprediction parameters, or set index information specifying one ofweighted prediction parameter sets.

In binarizing and encoding weighted prediction parameters, the smallestbinary codeword may be mapped to a weighted prediction parameter havingthe highest frequency of use statistically. For example, truncated unarybinarization may be performed on the weighted prediction parameter asshown in Table 1 below. Table 1 is an example in case of cMax is 6.

TABLE 1 Weighted prediction Index parameter Binary codeword 0 −1/4  111111 1 1/4 11110 2 3/8 110 3 1/2 0 4 5/8 10 5 3/4 1110 6 5/4 111110

The truncated unary binarization method shown in Table 1 is basicallythe same as a unary binarization method except that a conversion isperformed after receiving the maximum value (cMax) of the input inadvance. Table 2 shows the truncated unary binarization with cMax of 13.

TABLE 2 Value Binarization 0 0 1 1 0 2 1 1 0 3 1 1 1 0 . . . 12  1 1 1 11 1 1 1 1 1 1 1 0 13  1 1 1 1 1 1 1 1 1 1 1 1 1

During the weighted prediction parameter binarization, it is alsopossible to use different binary codewords depending on whether or notthe temporal directions of the reference pictures used for thebi-directional prediction are the same. For example, Table 3 illustratesbinary codewords according to whether or not the temporal directions ofthe reference picture L0 and the reference picture L1 are the same.

TABLE 3 Binary codeword when Binary bi-directional codeword whenprediction is bi-directional Weighted performed with prediction isprediction different performed with Index parameter directions samedirection 0 −1/4   111111 111110 1 1/4 11110 1110 2 3/8 110 10 3 1/2 0 04 5/8 10 110 5 3/4 1110 11110 6 5/4 111110 111110

It is also possible to determine the weight prediction parameter of thecurrent block according to a temporal order difference between thecurrent picture and the reference picture. Here, the temporal orderdifference may indicate encoding/decoding order difference betweenpictures or output order difference between pictures (e.g., a POCdifference value). For example, the weighted prediction parameter of thecurrent picture may be determined based on at least one of the POCdifference value between the current picture and the reference pictureL0 (hereinafter referred to as a first reference distance) and the POCdifference value between the current picture and the reference pictureL1 (hereinafter referred to as a second reference distance).

Specifically, the weighted prediction parameter of the current block maybe determined based on a ratio between the first reference distance andthe second reference distance. When the first reference distance is wand the second reference distance is h, w/(w+h) may be used as theweighted prediction parameter of the current block. For example, whenthe first reference distance and the second reference distance are thesame, the weighted prediction parameter of the current block may bedetermined as ½. In addition, when the first reference distance is 1 andthe second reference distance is 3, the weighted prediction parameter ofthe current block may be determined as ¼.

Alternatively, when the first reference distance is w and the secondreference distance is h, it is also possible to use a candidate weightedprediction parameter having a value most similar to w/(w+h) amongcandidate weighted prediction parameters as the weighted predictionparameter of the current block.

Alternatively, it is also possible to binarize the weighted predictionparameter of the current block in consideration of the first referencedistance and the second reference distance. Table 4 shows binarycodewords based on the first reference distance and the second referencedistance.

TABLE 4 When first When first reference reference distance distance andsecond and second reference reference distance distance are are Whenfirst different different reference (first (first distance is referencereference equal to distance = distance = Weighted second 2, second 1,second prediction reference reference reference Index parameter distancedistance 1) distance 2) 0 −1/4   111111 111110 111111 1 1/4 11110 111100 2 3/8 110 1110 110 3 1/2 0 10 10 4 5/8 10 0 1110 5 3/4 1110 110 111106 5/4 111110 111110 111110

In the example shown in Table 4, when the first reference distance andthe second reference distance are the same, the probability that theweighted prediction parameter will be set to ½ is high. As a result, thesmallest codeword may be assigned to ½ when the first reference distanceand the second reference distance are the same.

When the first reference distance and the second reference distance aredifferent, the smallest binary codeword may be mapped to the weightedprediction parameter that is statistically the most frequently used. Forexample, when the first reference distance is larger than the secondreference distance, the probability that a larger weight will beassigned to the reference picture L1 is high. Accordingly, the smallestbinary codeword may be mapped to the weighted prediction parameterlarger than ½. On the other hand, when the first reference distance issmaller than the second reference distance, the probability that alarger weight will be assigned to the reference picture L0 is high.Accordingly, the smallest binary codeword may be mapped to the weightedprediction parameter smaller than ½.

In contrast to the example shown in Table 4, it is also possible to mapthe smallest binary codeword to the weighted prediction parametersmaller than ½ when the first reference distance is larger than thesecond reference distance, and map the smallest binary codeword to theweighted prediction parameter larger than ½ when the first referencedistance is smaller than the second reference distance.

Even if a current block is similar to a reference block in a referencepicture, if there is a change in brightness between a current pictureand a previous picture, efficiency of intra prediction or interprediction may be decreased. Accordingly, it is possible to considerillumination compensation for compensating a prediction sample generatedthrough the intra prediction or the inter prediction or a reconstructionsample reconstructed based on the prediction sample for the change inbrightness between the current picture and the reference picture. Theillumination compensation may be performed by applying an illuminationcompensation weight and an offset to an image that is encoded/decoded inthe intra prediction or the inter prediction. For example, theillumination compensation prediction may be performed based on Equation3 below.p′=l×p+f  [Equation 3]

In Equation 3, p may denote the predicted sample encoded/decoded by theintra prediction or the inter prediction. l denotes the illuminationcompensation weight, and f denotes the offset. p′ may denote a weightedprediction sample to which the illumination compensation is applied.

It is also possible to apply the illumination compensation to thereconstruction sample obtained based on the prediction sampleencoded/decoded in the intra prediction or the inter prediction.Specifically, the illumination compensation may be applied to thereconstruction sample before an in-loop filter is applied, or to thereconstruction sample after the in-loop filter is applied. In this case,in Equation 3, p may denote the reconstruction sample and p′ may denotea weighted reconstruction sample to which the illumination compensationis applied.

An illumination change may occur across the entire area of a currentpicture or a current slice when comparing it with a previous picture ora previous slice. Accordingly, the illumination compensation may beperformed in units of a sequence, a picture or a slice.

Alternatively, the illumination change may occur only in a partial areawithin a slice or a sequence when comparing it with a previous slice ora previous sequence. Accordingly, the illumination compensation may beperformed in units of a predetermined area in a picture or a slice. Thatis, by determining whether or not to perform the illuminationcompensation in units of a predetermined area, it is possible to performthe illumination compensation only on a partial area, in which theillumination change is occurred, in a picture or in a slice.

When the illumination compensation is performed only for thepredetermined area within a picture or a slice, information fordetermining an area where the illumination compensation is performed maybe encoded/decoded. For example, information indicating a position ofthe area where the illumination compensation is performed, a size of thearea where the illumination compensation is performed, or a shape of thearea in which the illumination compensation is performed may beencoded/decoded.

Alternatively, it is also possible to encode/decode informationindicating whether or not the illumination compensation is performed inunits of a block. The information may be a flag of 1 bit, but is notlimited thereto. For example, whether or not to perform the illuminationcompensation may be determined in units of a coding tree unit, a codingunit, a prediction unit, or a transform unit. Accordingly, theinformation indicating whether to perform the illumination compensationmay be determined in units of a coding tree unit, a coding unit, aprediction unit, or a transform unit.

It is also possible to determine the area, in which the illuminationcompensation is performed, in a picture or a slice, and then determinewhether to perform the illumination compensation for each of blocksincluded in the area. For example, when the predetermined area includesa plurality of coding tree units, a plurality of coding units, aplurality of prediction units or a plurality of transform units,information indicating whether or not to perform the illuminationcompensation for each block included in the predetermined area may besignaled. Accordingly, the illumination compensation may be selectivelyperformed for each of the blocks included in units of to perform theillumination compensation.

Based on the above description, the illumination compensation predictionmethod according to the present invention will be described in detail.

FIG. 15 is a flowchart of a method of illumination compensationprediction according to the present invention.

First, an illumination compensation parameter for a current block may bedetermined S1510. The illumination compensation parameter may include atleast one of an illumination compensation weight or an offset.

The illumination compensation parameter may be signaled through abitstream in units of a sequence, a picture, a slice, or anencoding/decoding block. Here, the unit of the encoding/decoding blockmay represent at least one of a coding tree unit, a coding unit, aprediction unit, or a transform unit.

Alternatively, it is also possible to signal the illuminationcompensation parameter for each predetermined area in which illuminationcompensation is performed. For example, the illumination compensationparameter may be signaled for a predetermined area including a pluralityof blocks. The plurality of blocks included in the predetermined areamay use the same illumination compensation parameter.

The illumination compensation parameter may be signaled regardless of anencoding mode of the current block. Alternatively, whether or not tosignal the illumination compensation parameter may be determinedaccording to the encoding mode of the current block. For example, theillumination compensation parameter may be signaled only when theencoding mode of the current block has a predefined mode. Here, theencoding mode may indicate whether the current block is encoded in intraprediction (i.e., intra prediction mode) or whether the current block isencoded in inter prediction (i.e., inter prediction mode). For example,the illumination compensation parameter may be signaled only when thecurrent block is encoded with inter prediction. Alternatively, it isalso possible that the encoding mode may indicate one of a skip mode, amerge mode, an AMVP mode, or a current picture referencing mode, whichare inter prediction methods of the current block. Here, the currentpicture referencing mode represents an inter prediction method in whicha current picture including the current block is used as a referencepicture. When the current picture referencing mode is used, a predictionblock of the current block may be derived from an area reconstructedprevious to the current block. It is also possible to classify thecurrent picture referencing mode as one of intra prediction modes ratherthan the inter prediction mode. Alternatively, the current picturereferencing mode may be understood to be one embodiment of a skip mode,a merge mode, or an AMVP mode.

As an example, when the current block is encoded with the skip mode orthe current picture referencing mode, the illumination compensationparameter may not be signaled. On the other hand, when the current blockis encoded with the merge mode or the AMVP mode, the illuminationcompensation parameter may be signaled through the bitstream. If theillumination compensation parameter is not signaled, the illuminationcompensation for the current block may not be performed. Alternatively,if the illumination compensation parameter is not signaled, theillumination compensation of the current block may be performed usingthe illumination compensation parameter predefined in theencoder/decoder.

The illumination compensation parameter may be derived based on anillumination change between a first template area in the current pictureand a second template area in the reference picture. The first templatearea may be adjacent to the current block, and the second template areamay be adjacent to a reference block. Here, the reference block is usedto generate the prediction block of the current block, and may bespecified by a motion vector of the current block. Alternatively, thesecond template area may have a position co-located with the firsttemplate area in the reference picture. The position of the secondtemplate area may be variably determined in accordance with thereference picture or encoding mode of the current block.

When an unavailable sample is included in the second template area, areplacement value may be assigned to the unavailable sample using anavailable sample. For example, the available sample may be copied to aposition of the unavailable sample, or an interpolated value calculatedusing a plurality of available samples may be assigned to the positionof the unavailable sample. The available sample may be included in thesecond template region or may be located outside the second templateregion. For example, the replacement value of the unavailable sampleincluded in the second template area may be calculated based on theavailable sample included in the reference block. At least one of afilter coefficient, a shape, or the number of filter taps of a filterused in the interpolation may be variably determined based on at leastone of a size or a shape of the template region.

The illumination compensation parameter may be calculated based on adifference value between samples included in the first template regionand samples included in the second template region. For example, when aneighboring sample of the current block is assumed as yi (i is 0 to N−1)and a neighboring sample of the reference block is assumed as xi (i is 0to N−1), the illumination compensation weight l and the offset f may bederived by calculating the minimum value of E (w, f) in Equation 4.E(w,f)=Σ_(i)(p _(i)−(lp _(i) −f))²+λ(w−1)²  [Equation 4]

Equation 4 can be modified as following Equation 5.

$\begin{matrix}{{\begin{pmatrix}{{\Sigma_{i}x_{i}x_{i}} + \lambda} & {\Sigma_{i}x_{i}} \\{\Sigma_{i}x_{i}} & {\Sigma_{i}1}\end{pmatrix}\begin{pmatrix}l \\f\end{pmatrix}} = \begin{pmatrix}{{\Sigma_{i}x_{i}y_{i}} + \lambda} \\{\Sigma_{i}y_{i}}\end{pmatrix}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

From Equation 5, Equation 6 for deriving the illumination compensationweight l and Equation 7 for deriving the offset f can be derived.

$\begin{matrix}{l = \frac{{N\;\Sigma_{i}x_{i}y_{i}} - {\Sigma_{i}x_{i}\Sigma_{i}y_{i}} + \lambda}{{N\;\Sigma_{i}x_{i}x_{i}} - {\Sigma_{i}x_{i}\Sigma_{i}x_{i}} + \lambda}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack \\{f = {{\Sigma_{i}y_{i}} - {a^{*}\Sigma_{i}x_{i}}}} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

If the illumination compensation parameter is determined, theillumination compensation for the current block may be performed usingthe determined illumination compensation parameter S1520. Theillumination compensation may be performed by applying the illuminationcompensation weight and the offset to a block (e.g., a prediction blockor a reconstruction block) that is encoded/decoded in the intraprediction or the inter prediction.

When the inter prediction direction of the current block indicates aplurality of directions, compensation may be performed on at least oneof a plurality of prediction blocks, and a multi-directional predictionmay be performed on the current block based on the prediction block towhich the illumination compensation is applied. For example, if thebi-directional weighted prediction is applied to the current block, theillumination compensation may be performed on at least one of a firstprediction block and a second prediction block, and then, a finalpredicted block or a bi-directionally predicted block of the currentblock may be generated based on the weighted sum operation between thefirst prediction block and the second prediction block.

FIG. 16 is a flowchart of a bi-directional weighted prediction methodbased on illumination compensation.

Referring to FIG. 16, first, it may be determined whether or not theillumination compensation is performed on a reference picture S1610.Whether or not the illumination compensation is performed on thereference picture may be determined based on information signaledthrough a bitstream. The information may be a 1-bit flag, but is notlimited thereto. For example, pred_is_comp_flag may indicate whether ornot the illumination compensation is performed on the reference picture.

If it is determined that the illumination compensation is to beperformed on a reference block, the reference picture to which theillumination compensation is to be performed may be determined S1620.Specifically, when it is determined that the illumination compensationis performed on the reference block, it is possible to determine whetherto perform the illumination compensation on a reference picture L0 or toperform the illumination compensation on a reference picture L1. Thedetermination may be performed based on information signaled through thebitstream. The information may specify either one of the referencepictures. Alternatively, the information may be a plurality of 1-bitflags indicating whether or not the illumination compensation isperformed on each reference picture. For example, at least one ofpred_ic_comp_l0_enabled_flag indicating whether the illuminationcompensation is performed for the reference picture L0 orpred_ic_comp_l1_enabled_flag indicating whether the illuminationcompensation is performed on the reference picture L1 may be signaledthrough the bitstream.

If the reference picture on which the illumination compensation will beperformed is determined, an illumination compensation parameter to beapplied to the reference picture may be determined S1630. Since thedetermination of the illumination compensation parameter has beendescribed in detail with reference to FIG. 15, a detailed descriptionthereof will be omitted in this embodiment.

Based on the determined illumination compensation parameter, theillumination compensation may be performed on a prediction blockgenerated based on the reference picture on which the illuminationcompensation is to be performed S1640. Then, the bi-directional weightedprediction for the current block may be performed using the illuminationcompensated prediction block S1650.

FIG. 17 is a diagram illustrating an example of performingbi-directional weighted prediction using a prediction block to whichillumination compensation is applied. In FIG. 17, it is illustrated thatthe illumination compensation has been performed on a prediction blockgenerated based on a reference picture L1. Accordingly, thebi-directional weighted prediction for the current block may beperformed based on weighted sum of a prediction block P0 generated basedon a reference picture L0 and the illumination compensated predictionblock (l*P1+f) generated based on the reference picture L1.

It is also possible to perform the bi-directional weighted predictionfor the current block based on an illumination compensation weight usedfor the illumination compensation.

As an example, based on the illumination compensation weight, a weightedprediction parameter of the current block may be derived to perform thebi-directional weighted prediction on the current block. At this time,the weighted prediction parameter w of the current block may be set tothe same value as the illumination compensation weight l, or may be setto (1−l). For example, when the illumination compensation based on theillumination compensation weight I is applied to the prediction blockgenerated based on the reference picture L0, the bi-directional weightedprediction for the current block may be calculated based on thefollowing Equation 8.P(x)=l×P ₀(x)+f+(1−l)*P ₁(x)  [Equation 8]

As an example, it is also possible to perform the bi-directionalweighted prediction of the current block by applying a weight determinedby the weighted prediction parameter to one of the plurality ofprediction blocks and applying the illumination compensation weight tothe other. For example, the bi-directional weighted prediction for thecurrent block may be calculated based on Equation 9 below.P(x)=l×P ₀(x)+f+w*P ₁(x)  [Equation 9]

Although the above-described embodiments have been described on thebasis of a series of steps or flowcharts, they do not limit thetime-series order of the invention, and may be performed simultaneouslyor in different orders as necessary. Further, each of the components(for example, units, modules, etc.) constituting the block diagram inthe above-described embodiments may be implemented by a hardware deviceor software, and a plurality of components. Or a plurality of componentsmay be combined and implemented by a single hardware device or software.The above-described embodiments may be implemented in the form ofprogram instructions that may be executed through various computercomponents and recorded in a computer-readable recording medium. Thecomputer-readable recording medium may include one of or combination ofprogram commands, data files, data structures, and the like. Examples ofcomputer-readable media include magnetic media such as hard disks,floppy disks and magnetic tape, optical recording media such as CD-ROMsand DVDs, magneto-optical media such as floptical disks, media, andhardware devices specifically configured to store and execute programinstructions such as ROM, RAM, flash memory, and the like. The hardwaredevice may be configured to operate as one or more software modules forperforming the process according to the present invention, and viceversa.

INDUSTRIAL APPLICABILITY

The present invention may be applied to electronic devices which is ableto encode/decode a video.

The invention claimed is:
 1. A method for decoding a video, the methodcomprising: obtaining a first prediction block of a current block usingan L0 reference picture of the current block; obtaining a secondprediction block of the current block using an L1 reference picture ofthe current block; and obtaining a bi-predicted block of the currentblock based on a weighted sum operation of the first prediction blockand the second prediction block, wherein if a size of the current blocksatisfies a pre-defined condition, a first weight applied to the firstprediction block and a second weight applied to the second predictionblock are determined to be the same, wherein if the size of the currentblock does not satisfy the pre-defined condition, the first weight andthe second weight are determined based on index information specifyingone among a plurality of weight candidates, and wherein a number of theweight candidates is varied depending on temporal directions of the L0reference picture and the L1 reference picture.
 2. The method of claim1, wherein the first weight applied to the first prediction block isderived by subtracting the second weight from a constant value, andwherein the second weight applied to the second prediction block isdetermined to be a weight candidate specified by the index information.3. The method of claim 1, wherein the number of the weight candidates isdifferent between when both of temporal directions of the L0 referencepicture and the L1 reference picture are previous to or subsequent to acurrent picture, and when temporal directions of the L0 referencepicture and the L1 reference picture are different from each other.
 4. Amethod for encoding a video, the method comprising: obtaining a firstprediction block of a current block using an L0 reference picture of thecurrent block; obtaining a second prediction block of the current blockusing an L1 reference picture of the current block; and obtaining abi-predicted block of the current block based on a weighted sumoperation of the first prediction block and the second prediction block,wherein if a size of the current block satisfies a pre-definedcondition, a first weight applied to the first prediction block and asecond weight applied to the second prediction block are determined tobe the same, wherein if the size of the current block does not satisfythe pre-defined condition, the first weight and the second weight aredetermined based on one among a plurality of weight candidates, indexinformation specifying the determined weight candidate being encoded ina bitstream, and wherein a number of the weight candidates is varieddepending on temporal directions of the L0 reference picture and the L1reference picture.
 5. A non-transitory computer-readable medium whichwhen executed by a processor cause the processor to: obtain a firstprediction block of a current block using an L0 reference picture of thecurrent block; obtain a second prediction block of the current blockusing an L1 reference picture of the current block; and obtain abi-predicted block of the current block based on a weighted sumoperation of the first prediction block and the second prediction block,wherein if a size of the current block satisfies a pre-definedcondition, a first weight applied to the first prediction block and asecond weight applied to the second prediction block are determined tobe the same, wherein if the size of the current block does not satisfythe pre-defined condition, the first weight and the second weight aredetermined based on one among a plurality of weight candidates, indexinformation specifying the determined weight candidate being encoded ina bitstream, and wherein a number of the weight candidates is varieddepending on temporal directions of the L0 reference picture and the L1reference picture.